Author Topic: Boot BIOS-only OS on UEFI without CSM  (Read 675 times)

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Offline Logan

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Boot BIOS-only OS on UEFI without CSM
« on: June 15, 2021, 10:46:57 am »
Hi guys.
I want to boot an OS that only have BIOS compatibility, on a system that only have UEFI, is it possible? I just tried to boot it directly and it doesn't work. Can I use some multi-stage boot loader like GRUB to chain-loading it?
Thanks.
 

Offline eti

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Re: Boot BIOS-only OS on UEFI without CSM
« Reply #1 on: June 24, 2021, 11:29:44 pm »
Hi guys.
I want to boot an OS that only have BIOS compatibility, on a system that only have UEFI, is it possible? I just tried to boot it directly and it doesn't work. Can I use some multi-stage boot loader like GRUB to chain-loading it?
Thanks.

Although people here are very capable, I feel you'd be better served seeking help on a Windows specific forum.
 

Offline true

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Re: Boot BIOS-only OS on UEFI without CSM
« Reply #2 on: June 25, 2021, 12:56:48 pm »
To be honest most people are far less competent on those kinds of forums than here.

I haven't seen this done, and using a couple search engines, I can't really find any results for this either. If I wasn't slammed I'd try working on it / writing some code to emulate BIOS and play around. However it isn't as trivial as "load BIOS blob and run it" - I mean it almost could be for some tasks but for enough compatibility it would take some work.
 

Offline RaymondMack

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Re: Boot BIOS-only OS on UEFI without CSM
« Reply #3 on: July 06, 2021, 05:36:21 am »
Unless there is some sort of trick with using the bootloader from another UEFI compliant OS I doubt this will be easy to do without invoking the CSM. You may also run into issues if the HDD/SSD is formatted as GPT (GUID partition table) rather than MBR (master boot record).

If you specified what OS are you are trying to boot into you will likely get better help than a generic question.

Personally, I would just use a virtual machine to run the legacy OS inside a UEFI compliant OS. If you have thunderbolt and a thunderbolt video card (say from a dock) you can have native full speed graphics support inside the virtual machine. Though it is quite complicated to get working.

On a side note, I remember that Windows 7 was unable to run on my Surface Pro 3 due to it not supporting the newer UEFI standards that dealt with the video bios during booting. I can't remember what exactly would be required to make it work, but it was certainly beyond me at the time and no ready made solutions existed. If you are attempting something similar, you may as well give up and use Linux or Windows 8.1/10/11.
 

Offline eti

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Re: Boot BIOS-only OS on UEFI without CSM
« Reply #4 on: July 07, 2021, 12:38:24 am »
To be honest most people are far less competent on those kinds of forums than here.

I haven't seen this done, and using a couple search engines, I can't really find any results for this either. If I wasn't slammed I'd try working on it / writing some code to emulate BIOS and play around. However it isn't as trivial as "load BIOS blob and run it" - I mean it almost could be for some tasks but for enough compatibility it would take some work.

That is true, however, I meant that on Windows/PC-centric forums, they are doing these tasks ALL the time - it's second nature to them, ergo a solution would likely come to mind a little faster than here, and will likely have been tested by a wider audience, their member base, what with the members spending disproportionate amounts of time fiddling with Windows and UEFI.
 


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